With the new firmware if I stop reading at any point within a chapter and return to the home screen or power off and back on, the book opens at the beginning of the chapter. I thought maybe it had just corrupted the current book I was on, but it happens with another book I've never read before.

These are sideloaded books on an SD card. I've done a basic reset, but I will never do a factory reset until Kobo saves my stats for non kepubs in the cloud. I do not want to lose total time read.

On top of this, I can't sideload new books. The Kobo processes content but they never appear in the library.

I haven't had that problem but then I refuse to upgrade past 1.9.17 anymore. Having said that I do have an issue where my Kobo goes back a page, sometime although very rare it will go back 2 pages when it goes to sleep or powers off. Never had it go back to the start of a chapter though. Possible the bug has gotten worse in the new firmware?

I've done a basic reset, but I will never do a factory reset until Kobo saves my stats for non kepubs in the cloud. I do not want to lose total time read.

On top of this, I can't sideload new books. The Kobo processes content but they never appear in the library.

The fact that you're bookmarks aren't working and you can't load new books would suggest you have a corrupted database. In that case you may be stuck doing a factory reset to get things working properly. I know someone has posted before about the issue of it going back to start of chapter but it's not a common issue.

All I want to keep is the stat that says I've read for 290 hours...
I think for now I'll avoid any resets that could wipe this until it's saved into the cloud or perhaps in the new year. The books that were on my SD card before the update can still be read, and the bookmark issue is just a minor annoyance for now...

I don't know about the stats cus I don't pay any attention to them but I've had that weird chapter problem with 2.0.0 and with 2.0.4. So far, it hasn't started again with 2.1.5. The solution I had was to do a factory reset. That solved the problem until Kobo came out with 2.0.4 when I had to do it again.